[Shomaz ul Haq]

Dear all,

Hello. Hope all are well. What is the accurate and best way from the following to plot average outlet (plane) temperature of pipe?

1. ave(T)
2. areaAve(T)
3. lengthAve(T)
4. massFlowAve(T)
4. volumeAve(T)

I have used areaAve and massFlowAve. areaAve gives a very high value and massFlowAve gives a smaller value. What gives an accurate value? Would be grateful for answers. Also I read massFlowAve(T)@Outlet is often better than areaAve(T)@Outlet as the mass flow average is proportional to the heat flux leaving the domain (for constant properties fluids). Hope to hear from someone. Thanks.

[ghorrocks]

All those methods are completely accurate. They just tell you different numbers. Your question should be which is more meaningful - of course that depends on what you are trying to do.

But for most cases you are measuring the outlet temperature to get an idea of the energy lost from the system at that outlet. The energy leaving the system is the integral over the outlet of (density*area*normal velocity)*Cp*T. density*area*velocity is mass flow rate, so this is massflowAve(Cp*T). If Cp is constant this becomes Cp*massflowAve(T). If you don't care about the actual energy content and only care about a representative temperature then massflowAve(T) is the one to go with.

[Shomaz ul Haq]

Once again thanks a lot Glenn for this excellent advice. Appreciated!!!

[Shomaz ul Haq]

Actually I want to calculate energy received by the working fluid i.e. m_dot*c_p*(T_out-T_in) so that I can calculate the eta (thermal efficiency) of the system. I followed what you said and calculated Cp*(massFlowAve(T)@Outlet-massFlowAve(T)@Inlet). But I get a very big value with unts J/kg whereas it should be J/s or kg(m^2)(s^-3) or W. Can you tell me how can I calculate it correctly? Would be grateful. Thanks.

[ghorrocks]

I should correct my previous post - density*area*velocity is mass flow rate, so that means massflowAve is a good basis to normalise for the average. It does not mean massflowAve(T) equals the mass flow rate.

As long as your device is operating at steady state then massflow()@(inlet or outlet)*Cp*(massFlowAve(T)@Outlet)-massflowAve(T)*Inlet) should be better.

[Shomaz ul Haq]

Got it this time. Thanks!!!